Many semiconductor processing techniques use precursors or reactants which have been stored/shipped in ampoules. These precursors or reactants can gases, but are commonly solid or liquids. As many deposition processes, or etch processes, and the like, are gas phase interactions with a substrate surface, it is necessary to evaporate or sublimate the precursors or reactants.
For example, a typical solid precursor would be sublimated using a carrier or purge gas. The carrier gas is passed into an ampoule containing the solid precursor. The solid precursor sublimates and passes, with the carrier gas, and into a processing chamber. Once the level of precursor in the ampoule has decreased below a certain level, the ampoule must be changed to provide a fresh supply of precursor.
Ampoules for use with processing chambers contain precursor materials that are typically solid or liquids. The precursor sublimates or evaporates and fills the headspace of the ampoule. The concentration of precursor in the headspace is dependent upon, amongst others parameters, the vapor pressure and the temperature of the precursor within the ampoule. A gas or liquid flowing through the ampoule will carry precursor molecules from the headspace out of the ampoule causing a decrease in the amount of precursor within the ampoule. Evaporative cooling causes a decrease in the temperature of the contents which causes a decrease in the vapor pressure of the precursor. As precursor is removed from the ampoule, the concentration of precursor flowing from the ampoule decreases because there is less precursor in the headspace.
Therefore, there is a need in the art for apparatus and methods to maintain the amount of precursor in the headspace of a precursor ampoule.